The invention relates to a rotary-piston machine, in particular a rotary-piston internal combustion engine of trochoid type having a housing composed of at least one shell and at least two parallel end pieces and traversed by an eccentric shaft mounted in the end pieces and perpendicular thereto. A polygonal liquid-cooled piston is rotatably mounted on the eccentric of the shaft. The piston contains cavities provided with at least one aperture near their radially inner portion. The eccentric shaft has an axial bore through which the liquid flows communicating by way of transverse holes with the bearing points and with at least one spray nozzle. The orifice of the spray nozzle is directed at the aperture of the cavities in the piston.
A rotary-piston combustion engine of the type under consideration is present in German Pat. No. 1,223,610 in that engine, the liquid serving to lubricate the bearings of the eccentric shaft and the piston is employed to cool the piston as well. The cooling of the piston is thus accomplished predominantly by the liquid directly injected into the piston cavities by way of the nozzle, and in smaller, less effective part by the fluid draining from the piston bearing. But since the nozzle has an open cross-section, liquid is delivered through the nozzle into the piston cavities at all times, independently of engine operating temperature and load. Especially after a cold start and in the warm-up phase, this may result in the occurrence of high fuel consumption and unfavorable exhaust properties. This is because the piston has a comparatively large surface giving off heat and the comparatively cool liquid delivered into the cavities will retard rapid attainment of operating temperature in said modes. Another disadvantage of that design, however, is that the constant supply of liquid through the nozzle into the cavities interferes with building up a sufficient liquid pressure to lubricate the shaft and piston bearings at low speeds and idling, especially when the engine is cold.
Another type of rotary piston engine is present in Japanese Pat. No. Des. 47-14481. In that engine, the feed passage in the eccentric shaft to supply liquid to the piston cavities is made to be closable at low temperatures. This setting is effected by an expansion element arranged in the piston. The element acts on a rotary slide surrounding the piston bearing bushing and obturates or exposes the supply passage according to the effect of temperature. However, function of such a control is not necessarily assured because the expansion element is continually subjected to the alternation of centrifugal and centripetal forces owing to the manner of its arrangement on the piston and, hence, to high mechanical stress. The expansion element has a limited service life due to the comparatively high piston temperature. Furthermore, the function of this device cannot be monitored, and in event of damage, it cannot be dismantled without much outlay. Likewise disadvantageous is the fact that the central bearing surface of the bushing in the piston is lost because of the rotary slide surrounding the bushing, which necessitates widening the bushing.